After upgrading Maverick to Yosemite on a MacbookPro, Firefox will not load. If another browser (Chrome or Safari) is open, it will open instead of FireFox. I have tried total reinstall of Firefox and other solutions (will not start in safe mode either) but no change. All that comes up at times is a black screen for a moment and then nothing. Most of the time the screen just freezes. Something is blocking Firefox from opening, any suggestions? Thanks